The Drosophila laboratory is currently engaged in four major lines gf research: (1) the genetic analysis of mutants affecting meiosis; (2) the analysis of several maternal-effect mutants; (3) the mechanism of segregation-distortion; and (4) studies on aging in Drosophila. With respect to point 1, the array of meiotic mutants collected in this laboratory now invodves about 35 loci and includes genes influencing the rate of recombination, the distribution of exchanges along the chromosome, the distribution of exchanges among chromosomes, the regularity of homologous centromere separation at anaphase I, the regularity of sister centromere separation at anaphase II, the ability of chromosomes to move to the anaphase poles, and the behavior of chromosomes in gametes and immediately upon fertilization. We are presently analyzing one meiotic mutant that causes a lesion early in meiosis in a process necessary for recombination, homologous segregation and nonhomologous pairing. In addition, we are about to search for new meiotic mutants in processes undetectable by the methods we had been using. With respect to point 2, we have analyzed the behavior of two closely-linked autosomal maternal-effect mutants whose phenotype has been shown to depend on the amount of sex-chromosome heterochromatin in the individuals involved. We are currently examining the proposition that there is a region on chromosome 2 that contains a set of linked genes all of which control the activity of sex chromosome heterochromatin. Our current thrust is to find more mutants in the suspect region to see if these too are maternal-effect genes dependent upon sex-chromosome heterochromatic gene activity. With respect to point 3, we have shown that the SD gene has the property that during meiosis it changes the homologous chromosome such that it becomes a gametic lethal. We are currently engaged in analyzing X-ray deletions of SD and also the region that responds to SD in an attempt ultimately to test biochemical models about the mechanism of segregation-distortion. With respect to point 4, we are currently engaged in a test of the Orgel hypothesis of aging using the Drosophila enzyme, catalase. We are also attempting to develop a morphological and biochemical phenotype of aging with the ultimate aim of isolating and analyzing aging mutants.